6.4.2 FSF-Copyrighted Package

If you are maintaining an FSF-copyrighted package, please don’t copy
in any code without verifying first that we have suitable legal papers
for that code.

If you are copying from another FSF-copyrighted package, then we
presumably have papers for that package’s own code, but you must check
whether the code you are copying is part of an external library; if
that is the case, we don’t have papers for it, so you should not copy
it. It can’t hurt in any case to double-check with the developer of
that package.

When you are copying code for which we do not already have papers, you
need to get papers for it. It may be difficult to get the papers if
the code was not written as a contribution to your package, but that
doesn’t mean it is ok to do without them. If you cannot get papers
for the code, you can only use it as an external library
(see External Libraries).